Recently, object detection devices including a stereo camera device, a laser radar device and the like, which detect an ambient object by processing distance information acquired by sensing the external, have been put into practical use. These object detection devices can be applied to a monitoring system to detect intrusion of a suspicious person, an abnormality, an in-vehicle system to support driving safety of a car, or the like.
An object at the front side which hinders driving is regarded as an obstacle, and it is possible to provide a function to avoid or alleviate collision using a means such as alarm or automatic braking in a case where there is a risk of collision with the obstacle in the in-vehicle system.
It is important to estimate a geometric position relationship of a road surface in order to accurately detect the obstacle and a position of the obstacle in the in-vehicle system. The road surface is almost reliably included in a sensing range in the environment of the in-vehicle system, which is because it is possible to narrow down an area in which the obstacle is present, for example, to regard an object detected on the road as the obstacle when it is possible to calculate the geometric position of the road surface. It is possible to reduce problems such as erroneous detection in which an obstacle is erroneously detected in a spatial area in which the obstacle is absent or non-detection in which an obstacle is not detected in a spatial area in which the obstacle is present by narrowing down an area in which the obstacle is present. Thus, it is important to accurately detect the road surface in order to accurately detect the obstacle.
PTL 1 is an example of the background art in the present technical field. PTL 1 discloses a technique of providing a road surface shape recognition device which is capable of accurately detecting an actual road surface shape not only in a case where a traffic lane is marked on a road surface but also in a case where the traffic lane is not marked. In addition, NPL 1 describes that “the computation of the free space computation has two main goals: 1. Find the distances to the closest objects. 2. Find the road surface segmentation. While finding the distance to objects aims at navigating the car or triggering safety systems, the second objective is probably of the same importance. It is crucial for the road surface estimation task described in the first part of this paper. The reason for this is that measurements on vehicles and other objects in crowded scenarios influence the B-spline curve and the resulting curve estimation may become unstable in such scenarios. Therefore, only 3D measurements in the free space are used for the spline estimation, neglecting all stereo measurements on objects”, and “how is the correct free space boundary found. The key idea is to inspect every individual image column u. A matching score is obtained, summing up a score which evaluates the likelihood of pixels belonging to the road surface from the bottom of the image up to the free space boundary v(d,u). A second matching score evaluates the fit of pixels belonging to objects with disparity d from the free space boundary in the image on upwards. The total score for an image row u and an obstacle at disparity d becomes: SCORE(u,d)=ROAD(u,d)+OBJECT(u,d). The best boundary match is given as the maximal score”.